1. Technical Field
The present invention relates generally to a communications system and in particular to a method and apparatus for routing data within the communications system. Still more particularly, the present invention relates to a method and apparatus for intercepting calls in a communications system.
2. Description of the Related Art
Many of the present digital telecommunications networks of the world are based on time-division multiple access (TDMA) and use transmission and switching products like digital switches and pulse coded modulation (PCM) transmission at E1 or T1 rates. TDMA users share the radio spectrum in the time domain. An individual user is allocated a time slot and, during this time slot, the user accesses the whole frequency band allocated to the system (wideband TDMA) or only a part of the band (narrow band TDMA). In TDMA, transmission take place in bursts from a mobile station to a base station in an uplink path with only one user transmitting to the base station at any given time. In the downlink path from the base station to the mobile station, the base station usually transmits continuously with the mobile station listening only during the assigned time slot. TDMA channel multiplexes the bids from a number of users. This type of system requires transmission at a higher bit rate over a radio frequency channel.
Another technology that is becoming more widely used is code-division multiple access (CDMA) in a spread spectrum. Spread spectrum techniques spread the bandwidth of the transmitting signal over a spectrum or band of frequency much larger than the minimal band with required to transmit the signal. CDMA has an ability to lock out conflicting signals, which may allow it to share a system with other radio signals without interference.
Wireless technology is an important component of the global information infrastructure. To exploit the full potential of this technology, regulators and administrators of all countries are re-evaluating their spectrum allocation policy. A large segment of the spectrum around two GHz bandwidth has already been released for the use of wireless networks. More spectrum is being allocated by the International Telecommunications Union (ITU) and countries like the United States of America and Canada around the 7-10 GHz range to use wireless technology for broadband wireless applications. Wireless networks are being built all over the world to handle a large volume of traffic and mobility.
With the increased demand for cellular telephones, manufacturers look for new technologies to overcome the problems of poor signals and battery performance. Poor signals resulted in poor performance for the user and a high frequency of false hand offs in the system. Better battery performance was needed to reduce size and costs of hand held units. The size of handsets and better battery performance led to low power designs and performance targets possible only using fully digital technologies. In particular, digital cellular systems based on the global system for mobile communications (GSM) using TDMA have emerged in Europe while systems based on IS-54 using TDMA and IS-95 using CDMA are being developed in the United States.
With this increase in use of wireless communication systems, security agencies have focused on methods for intercepting calls within the systems. Security agencies in the execution of their duties may be authorized to capture the call content of a targeted subject using telecommunications equipment. A GSM system provides mobile cellular service and is the equipment used by some carriers to provide mobile phone service to their subscribers. When an intended targeted subscriber is using cellular services provided by a GSM system, then the GSM system must have the necessary capability to recognize the target, capture call details and call content, and deliver them to the designated security agencies in real time. This type of capability is called "call interception".
Currently, in some call interception products available in GSM systems, complete activity of the target is not captured. For example, some products are not capable and do not capture handover activity. Additionally, the GSM technology is continuously evolving, providing new capabilities and services to mobile users on a regular basis. With this changing of GSM technology, the presently available call interception products usually have to be extensively modified to capture the new activity and a lag often occurs behind the delivery of the new service.
Therefore, it would be advantageous to have an improved method and apparatus for intercepting calls in a communication system.